1. Technical Field
The present disclosure relates to a method and system for controlling an engine clutch of a hybrid vehicle that may effectively select an engagement way of the engine clutch according to a state of the hybrid vehicle and a running state.
2. Background
Hybrid vehicles operate through the use of power from an internal combustion engine and power from a battery. In particular, hybrid vehicles are designed to efficiently combine and use the power of the internal combustion engine and a motor.
For example, as illustrated in FIG. 1, a typical hybrid vehicle includes: an engine 10; a motor 20; an engine clutch 30 which controls power transmission between the engine 10 and the motor 20; a transmission 40; a differential gear unit 50; a battery 60; an integrated starter-generator (ISG) 70 which starts the engine 10 or generates electric power by output of the engine 10; and wheels 80.
As further shown, the hybrid vehicle includes: a hybrid control unit (HCU) 200 which controls overall operation of the hybrid vehicle; an engine control unit (ECU) which controls operation of the engine 10; a motor control unit (MCU) 120 which controls operation of the motor 20; a transmission control unit (TCU) 140 which controls operation of the transmission 40; and a battery control unit (BCU) 160 which manages and controls the battery 60.
The battery control unit 160 may also be referred to as a battery management system (BMS). In the vehicle industry, the integrated starter-generator 70 may also be referred to as a starting/generating motor or a hybrid starter & generator.
The hybrid vehicle may run in a driving mode, such as an electric vehicle (EV) mode using only power of the motor 20, a hybrid electric vehicle (HEV) mode using torque of the engine 10 as main power and torque of the motor 20 as auxiliary power, and a regenerative braking (RB) mode during braking or when the vehicle runs by inertia. In the RB mode, braking and inertia energy are collected through power generation of the motor 20, and the battery 60 is charged with the collected energy.
The HEV mode and the EV mode depend on engagement or lock-up, or release or open of the engine clutch 30 installed between the engine 10 and the motor 20. In other words, the HEV mode is performed with an engagement state of the engine clutch 30, and the EV mode is performed with a release state of the engine clutch 30.
The engagement of the engine clutch 30 may include a sync engagement and a launch slip engagement.
As shown in FIG. 2, the sync engagement is performed by engaging the engine clutch 30 after synchronizing speed of both ends of the engine clutch 30, or after synchronizing speed of the engine 10 with speed of the motor 20.
While performing the sync engagement, until the engine clutch 30 is completely engaged, the motor 20 covers power requested in the hybrid vehicle.
The sync engagement may not be performed at a low speed, because if the sync engagement of the engine clutch 30 is done when speed of the motor 20 is less than a minimum speed, such as a minimum idle speed of the engine 10, engine stall may occur.
Since the sync engagement is performed after synchronizing speed of both ends of the engine clutch 30, the sync engagement provides an advantage in terms of durability of the engine clutch 30.
In the meantime, as shown in FIG. 3, the launch slip engagement is performed by supplying hydraulic pressure to the engine clutch 30 before speed of both ends of the engine clutch 30 is synchronized.
According to the launch slip engagement, slip torque may be transmitted as driving power before the engine clutch 30 is completely engaged.
As shown in FIG. 3, the launch slip engagement may be performed from when speed of the hybrid vehicle is low, for example, when the speed of the motor is 0.
Since the launch slip engagement generates more slip than the sync engagement, the launch slip engagement is not desirable in terms of durability of the engine clutch 30.
Further, while controlling the launch slip engagement, since compensation and correction for deviation and hydraulic pressure response and so on of the engine clutch 30 is needed, the launch slip engagement is inferior to the sync engagement in terms of drivability.
The sync engagement and the launch slip engagement are appropriately selected according to running state when the EV mode is changed to the HEV mode as running modes of the hybrid vehicle.
In a conventional hybrid vehicle, when the EV mode is changed to the HEV mode, if speed of the motor 20 is faster than speed of the engine 10, the sync engagement is performed. Otherwise, the launch slip engagement is performed.
In other words, in a conventional hybrid vehicle, even though it is possible to perform the sync engagement when the engine clutch is engaged, the launch slip engagement which is not desirable in durability and drivability is performed.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure.